<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>BFC</title>
    <style type="text/css">
        div.xiongda{
            border: 1px solid red;
        }
        div.box1{
            width: 200px;
            height: 200px;
            background-color: red;
            float: left;
        }
        div.box2{
            width: 500px;
            height: 200px;
            background-color: green;
            overflow: auto;
        }
    </style>
</head>
<body>
    <div class="xiongda">
        <div class="box1"></div>
        <div class="box2"></div>
    </div>
</body>
</html>